I haven't had any problem above -15C with my X2s. But if you can keep vents warm with hands etc. they are easier to close. My old ARX has rather hard vents when they get cold, but no problems with X2s. Be careful with the pump. It breaks easily when it is cold.

I use my foils only when it is under -15C. BUT I'm not kiting on mountains. Only on flat and no long "trips".

I also pump my struts hard so the kite turns fast and keeps its shape like in summer.

The reason why I fly inflatables is simple: I want to have the same experience on snow like in water. Good pop and lift in jumps and fast and powerful big kites in light winds. It is good practise for summer.

greetings from Canada. I was kiting today in -12c & 50km/hr winds = pretty cold windchill. The sun was out, but so much blowing snow at ground level, that the only thing you could see of the other kiters was the kites floating above the snow.

I don't think I would enjoy much colder: I think I'll forget about it if it gets to -15c!

Correct me if wrong please, but -15C is roughly equal to 5F, right? If that's true, anything below 40F seems to make inflatos hard to pump up. I was pumping up the slingshot 12m the other day (it was 15F). The valve rubber was hard and the pump wouldn't stay in the hole, so I had to hold it and pump. As the pressure in the LE became greater, it became more frustrating. Cold hands! I pumped the struts up prior to going out, so that helped. The kite works, but self launch on grass and landing is not easy.

Like I said I have not had any problems with the valves of my Naish X2s. They are softer than valves of ARX. I don't know Sligshots. -15C = 5F is cold if there is hard wind. But 10-14 knots with 20m2 X2 is nice if it is sunny. Just wear right kind of clothes that you don't sweat and get wet.

Especially, if you are not near sea or open water, then air is dry and moisture don't increase the wind chill.

Foils are one solution but if you like inflatables you can still use them if you have good valves. In -25C = -13F also I would select a big foil.

But this is just my experience. Here the winter is long and dark, so you have to do what kiteboarder have to do Kids, do not try this at home.